(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of fabricating a Schottky diode using a shallow trench structure to solve the leakage current problem in the fabrication of integrated circuits.
(2) Description of the Prior Art
The contact structure of a metal to a lightly doped silicon is known as a Schottky diode. Typically, Aluminum is the metal used. The aluminum material""s directly touching the silicon substrate within the contact hole often causes junction spiking. A barrier metal layer such as titanium tungsten, titanium nitride, or the like has been added between the silicide and the aluminum material to reduce junction spiking. A platinum silicide (PtSi) layer, for example, is formed between the Al and the barrier metal and the silicon substrate. The traditional contact structure requires a small amount of silicon loss in the silicide formation. However, this will increase the sensitivity of the Schottky diode to leakage caused by the metal pre-sputter etch. It is desired to find a method of making a Schottky diode structure without concern of junction leakage.
U.S. Pat. No. 4,835,580 to Havemann et al teaches a method of embedding a Schottky barrier diode within a bipolar transistor. They use a deep trench to increase diode area and decrease diode series and base-collector capacitance. U.S. Pat. No. 5,583,348 to Sundaram shows a method for forming a Schottky diode within a contact opening where a platinum silicide layer is deposited at the bottom of the opening. U.S. Pat. No. 5,166,094 to Kapoor teaches a method of forming Schottky diodes in base coupled transistor logic.
A principal object of the present invention is to provide an effective and very manufacturable method of fabricating a Schottky diode with reduced leakage current in the fabrication of an integrated circuit device.
Another object of the present invention is to provide an effective and very manufacturable method of fabricating a Schottky diode using a shallow trench contact to reduce leakage current in the fabrication of an integrated circuit device.
A further object of the invention is to provide a method of fabricating a Schottky diode using a shallow trench contact which leads to better silicide coverage of the contact opening thereby reducing junction leakage.
A still further object of the invention is to provide a method of fabricating a Schottky diode using a shallow trench contact obtained by an overetch of the traditional contact etch which leads to better silicide coverage of the contact opening thereby reducing junction leakage.
In accordance with the objects of this invention a method for fabricating a Schottky diode using a shallow trench contact to reduce leakage current in the fabrication of an integrated circuit device is achieved. A thermal oxide layer is provided overlying a silicon semiconductor substrate. An insulating layer is deposited overlying the thermal oxide layer. A contact opening is etched through the insulating layer and the thermal oxide layer to the silicon substrate. The contact opening is overetched whereby a shallow trench is formed within the silicon substrate underlying the contact opening wherein the shallow trench has a bottom and sidewalls comprising the silicon substrate. A first metal layer is deposited over the insulating layer and within the contact opening and within the shallow trench. The first metal layer is sintered whereby the first metal layer is transformed to a silicide layer where the silicide layer contacts the silicon substrate at the bottom and sidewalls of the shallow trench and wherein the first metal layer contacting the insulating layer and thermal oxide layer is not transformed. The untransformed first metal layer is removed. A barrier metal layer is deposited overlying the insulating layer and the silicide layer within the shallow trench. A second metal layer is deposited overlying the barrier metal layer to complete fabrication of a Schottky diode in an integrated circuit device.
Also in accordance with the objects of this invention, an improved Schottky diode in an integrated circuit device is described. A metal layer extends through an opening in an insulating layer contacting a silicon semiconductor substrate. A barrier metal layer underlies the metal layer within the opening. A metal silicide region within a shallow trench contacts the silicon semiconductor substrate at the bottom and sidewalls of the shallow trench underlying the barrier metal layer within the contact opening.